Abstract: Provided herein are methods and devices operable to monitor the hydration of a user. The wearable device for hydration monitoring includes an emitting component operable to emit light having at least three different wavelengths, a sensor operable to receive a reflected portion of the emitted light, and a processor operable to receive signals from the sensor. At least one of the wavelengths is in the range from 900 nm to 1600 nm for optical detection of a level of water. The method for hydration monitoring includes emitting light from a light emitting component operable to emit light having at least three different wavelengths and detecting light with at least one photodetector. At least three distances between the light emitting component and the photodetector are known and the at least three distances allow monitoring of at least two different tissue beds with at least two different tissue depths.